Stable isotopes of metals are increasingly being used in human health and nutrition research, and these new isotope tools are supplanting radiotracer use in several applications. The expanding use of stable isotope methods is being fueled by the development of new mass spectrometers that are capable of measuring stable isotope ratios of metals at very high precision. Precision is the key performance metric for stable isotope methods and the enhanced precision results in greatly improved statistical power in applications using enriched stable isotope tracers. Equally exciting is the recognition that natural mass-dependent isotope fractionation in biological systems can provide novel information about metal biochemistry and physiological processing; and latest generation of mass spectrometers have the capable to accurately quantify these very small changes in isotope ratios. We are requesting funding to purchase a multicollector inductively coupled plasma mass spectrometer (MC-ICPMS) which will support a large and diverse group of research projects where the use of mineral and trace element isotopes are critical to advance our understanding of disease processes. The instrument will be housed in the trace element clean room facility at the University of Wisconsin State Laboratory of Hygiene (WSLH), leveraging the unique infrastructure and expertise in inorganic mass spectrometry. The WSLH has a long history of effective management of its shared-instrument resources and will provide internal funding for additional staff and maintenance of the new instrument. The MC-ICPMS will support and enhance the core measurements and goals of the NIH-funded projects detailed in this application, expand capacity, and provide a foundation from which promising new isotope systematics and tools can be developed for biomedical research.